1. Field of the Invention
The present invention relates to a method of producing a microelectronic electrode structure, in particular for a PCM memory element, and to a corresponding microelectronic electrode structure.
2. Description of the Prior Art
Although in principle it can be applied to any desired microelectronic electrode structure, the present invention and the problems on which it is based are explained on the basis of PCM (phase change memory) memory elements.
U.S. Pat. No. 5,166,758 discloses a PCM (phase change memory) memory element in the case of which electrical energy is used for converting a PCM material, typically chalcogenide alloys (e.g. G2Sb2Te5), between the crystalline phase (high conductivity, logical “1”) and the amorphous phase (low conductivity, logical “0”).
The conversion from the amorphous phase into the crystalline phase requires a thermal pulse with a temperature which is higher than the glass transition temperature but lower than the melting temperature, whereas the conversion from the crystalline phase into the amorphous phase requires a thermal pulse with a temperature greater than the melting temperature followed by rapid cooling.
In the case of the above example of Ge2Sb2Te5, the melting temperature is about 600° C. and the glass transition temperature is about 300° C. The crystallisation time is typically around 50 ns.
PCM memory elements of this type have a whole series of advantageous properties, for example non-volatility, direct overwritability, non-destructive readability, rapid writing/erasing/reading, long service life (1012 to 1013 read/write cycles), high packing density, low power consumption and good integratability with standard semiconductor processes. In particular, the previously known concepts of SRAM, EEPROM and ROM can be combined in a PCM memory element.
One of the main problems with the known PCM memory elements is the relatively high heat generation during the programming and erasing operations. These problems are suitably remedied by reducing the contacted electrode area to increase the current density and consequently lower the energy consumption and the associated heat generation.
IEDM 200136,05, Stefan Lai and Tyler Lowrey, “OUM—A 180 nm Nonvolatile Memory Cell Element Technology for Stand Alone and Embedded Applications” provides a summary of the current state of development of PCM memory elements (also referred to there as “OUM” (Ovonic Unified Memory) memories) in 180 nm technology.